1. Field of the Invention
The present invention is generally related to spirobifluorene derivatives, and more particularly to synthesis of 2,2′-disubstituted 9,9′-spirobifluorene-based triaryldiamine.
2. Description of the Prior Art
In general, 2,2′-disubstituted 9,9′-spirobifluorene-based triaryldiamine are synthesized from 2,2′-dihalo-9,9′-spirobifluorene. For example, 2,2′-dibromo-9,9′-spirofluorene can be prepared by direct bromination of 9,9′-spirobifluorene in the presence of a catalytic amount of ferric chloride. However, there are much difficulty in the preparation and isolation of pure 2,2′-dibromo-9,9′-spirobifluorene. Alternatively, 2,2′-dibromo-9,9′-spirofluorene can be prepared by the replacement of amino group of 2,2′-diamino-9,9′-spirobifluorene by cupric bromide following conventional Sandmeyer procedure. In addition to biphenyl-, azobenzene-, and phenol-type side products, Sandmeyer reactions are often plagued with position isomers of halide substituent. In this case, 2,2′-dibromo-9,9′-spirobifluorene was obtained together with 2,3′-dibromo-9,9′-spirobifluorene and 2,2′,3′-tribromo-9,9′-spirobifluorene as well, and the separation of these isomers remains difficult and greatly hampers materials applications. Therefore, new method of forming 2,2′-disubstituted amine-9,9′-spirobifluorenes is still needed corresponding to obtain more pure compound, improve the yield and reduce manufacturing cost.